Shrink bag with non-shrink header

ABSTRACT

A heat shrinkable bag having a non-shrink header for containing a product. The bag includes first and second side walls formed from heat shrinkable material joined together to form a body portion having an opening for access into an interior chamber having an inner surface to receive and contain the product. A header is attached to the inner surface of the body portion and extends outwardly from the opening in the body portion. The header is substantially formed from non-shrinkable film material that prevents distortion of the header during manufacture of the bag.

FIELD OF THE INVENTION

[0001] The present invention relates generally to the packaging industry and, more particularly, to wicketed, side sealed heat shrinkable bags manufactured for the packaging of fresh and frozen food products.

BACKGROUND OF THE INVENTION

[0002] Conventional wicketed, side sealed heat shrinkable bags, manufactured for the packaging of fresh and frozen food products packaged in foam trays, are fabricated from a single component heat shrinkable polyolefin material. These bags are generally formed by folding a single sheet of material onto itself and heat sealing the sides to form an open-ended bag. The single sheet of material is folded such that a single-layer lip or header extends beyond the open compartment formed between the sides of the bag. The lip or header contains wicket holes and allow the bags to be stacked in a pile on top of hole guides or wickets.

[0003] One significant drawback of these conventional single material heat shrinkable bags is that the heat used to secure the side seals of the bags also distorts and heat stresses the bag in the region near the seals and in the area where there is only a single layer of material at the top lip or header of the bag. This may result in bag failures either during manufacture of the bag or use of the bag.

[0004] For example, during the heat-sealing phase of the bag manufacturing process, a conventional wicketed heat shrink bag will curl and slightly alter its position on the bag making machine due to the effects of the heat. As the bag advances forward on the machine, it is picked up by vacuum arms that transfer the bag to the stacking section where the wicket holes in the header of the bag are supposed to line up with pins mounted on the stacking section. If the bag under construction has shifted, the alignment of the holes is off, causing some of the bags not to be stacked on the pins. The misaligned bags eventually fall off the stacker section and end up as scrap.

[0005] The conventional shrink bag that has been effected by the heat stress caused at the time of bag manufacture also causes problems during product loading. The shrink bags typically do not lay flat on the bag loading equipment because the heat applied to the film during bag manufacture cause the sides of the bag header to curl up. These curled headers conflict with the bag loader opening devices (product guides). If the product does not enter into the bag smoothly, the product may snag the sides of the bag, making it come off prematurely, resulting in improperly wrapped products.

[0006] In addition, the conventional shrink bag made for the packaging of fresh and frozen food is typically made of a material that has a high coefficient of friction, resulting in bags that have a tendency to cling together and be difficult to open for the insertion of the product.

[0007] Furthermore, the conventional shrink bag is made from a material that has been electronically cross linked, or irradiated, to a level where the tear resistance of the material is high and when cut, punctured, or slit, the resultant tear will not propagate along a straight line. Typically, the bag is manufactured with a slit above the wicket hole on the lip of the bag to provide a path for a tear to follow as the bag is removed from a wicket wire or post on a bag loader. At times, due to the crosslinking, the tear will not follow the path created by the slit. Instead, the tear will propagate outwardly or in direction diagonal to the slit and a portion of material will be left behind on the wicket wire or loader post as the bag is removed. This portion, or “chaff”, as it is known, will cling to the wire or the post, causing difficulties in the continuance of bag loading. One problem is the undesirable possibility that the loose chaff can be blown into subsequent bags being loaded with product, or blown into or onto the packaging equipment or work area, creating the need for additional cleaning. Another problem is that the chaff will have a tendency to cling to the next bag being opened, sometimes causing it to tear unevenly, whereby multiple portions of chaff can be produced. The bag loading process must be stopped to remove the chaff, reducing operational efficiency.

[0008] Accordingly, there is a continuing need for an improved heat shrinkable bag fabricated in a manner that reduces or eliminates bag failures caused by the heat stress and undesirable material tendencies. A preferable bag would include a stiff header that does not shift or curl when contacted by heat, thereby avoiding the misalignment with the stacking pins. Also, a preferable bag would open easily and be released from the wicket cleanly during the loading operation. Desirably, the improved heat shrinkable bag would allow for more efficient production in the manufacture of the bag, and reduced loss of bags and product at the packager.

SUMMARY OF THE INVENTION

[0009] In accordance with the present invention, a heat shrinkable bag for containing a product includes first and second side walls formed from heat shrinkable material and joined together to form a body portion having an opening for access into an interior chamber having an inner surface to receive and contain the product. The first and second side walls are preferably formed from a single sheet of heat shrinkable polyolefin film that is folded over upon itself to form a fold at one end. The edges of the first and second side walls may then be attached, e.g., heat sealed, to each other to form the body portion. A header is attached to the body portion and extends outwardly from the opening in the body portion. The header is substantially formed from non-shrinkable film material that prevents distortion of the header during manufacture of the bag. Preferably, the header is attached to the inner surface of the interior chamber such that a portion of the header extends down into the interior chamber of the body portion. The header may be attached to the inner surface of the body portion using a thin longitudinal heat seal.

[0010] The present invention also includes a method for producing a heat shrinkable bag for containing a product. The method includes folding a single sheet of heat shrinkable polyolefin film over upon itself to form first and second side walls. The film is folded in a manner to create a lip in the second side wall extending above the top edge of the first side wall. A header is then attached to the lip along a thin longitudinal heat seal such that the header extends outwardly from the side walls. The header is preferably substantially formed from non-shrink material that prevents distortion of the header during manufacture of the bag. Heat and pressure are then applied to seal two edges of the side walls to form a body portion that has an opening for access into an interior chamber to receive and contain the product.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] To facilitate further discussion of the invention, the following drawings are provided in which:

[0012]FIG. 1 is a perspective view of the improved heat shrinkable bag of the present invention;

[0013]FIG. 2 is a side view of the presently preferred heat shrinkable bag having a non-shrink header; and

[0014]FIG. 3 is an illustration of a bag making machine, which may be used to fabricate the improved heat shrinkable bag of the present invention.

[0015] These drawings are for illustrative purposes only and should not be used to unduly limit the scope of the claims.

DETAILED DESCRIPTION OF THE INVENTION

[0016]FIGS. 1 and 2 illustrate a heat shrinkable bag 10 of the present invention that is preferably designed to contain a product such as fresh and frozen foodstuffs. The body portion 20 of the bag 10 is formed from a single sheet of film material that is folded over upon itself forming two side walls 20 a and 20 b along fold line 24 and then heat sealed along edges 22 a and 22 b. Alternatively, the body portion 20 may be formed from two separate sheets of film material that are heat sealed to each other along three edges thereof.

[0017] The folded-over film forms a first side wall 20 a and a second opposing side wall 20 b. The single sheet of film material is preferably folded over onto itself along a fold line 24 such that one side wall of the bag extends slightly beyond the other side wall to form a lip 16. If desired, the lip 16 can be eliminated. The top edges of the side walls 20 a and 20 b form an opening allowing access to an interior chamber of the bag 10 for containing products.

[0018] Suitable materials for the film material used for the side walls 20 a and 20 b of the bag 10 typically include pliable films which are strong and fluid impermeable. In accordance with the preferred embodiment of the present invention, suitable materials include polymeric films, such as polyolefin films, including such representative examples as biaxially-oriented, heat-shrinkable, linear low density polyolefins. Other suitable materials may include films of low and linear low density polyethylenes, oriented polypropylene, nylon, and polyester.

[0019] The bag 10 includes a header 12 attached to the body portion 20 that extends outwardly from the opening in the body portion 20. Preferably, the header 12 is substantially formed from non-shrink material that prevents distortion of the header 12 during manufacture of the bag 10. The header 12 replaces or supplements the conventional shrink material header or lip found in conventional heat shrink bags. The header 12 extends above the lip 16 of the bag 10 and also extends down into the interior chamber of the bag 10, thus creating an improved high slip surface for the lip 16. As an example, the header 12 may extend about 1½-2 inches above the lip 16 and extend about ½-1 inch into the interior chamber of the body portion 20. Having the header 12 extend down into the interior chamber creates a stronger seal at the point where the header 12 is attached to the body portion 20 at side seals 22 a and 22 b. In some embodiments, the header 12 may extend down further into the interior chamber of the body portion 20, thus providing a stronger seal further down into the interior chamber at side seals 22 a and 22 b. This will increase the seal strength in the top portion of the bag above what is expected from the base material alone. Some bag loading machines and hand loading processes are subject to swings in the amount of outward force applied to the bag opening devices when in contact with side seals 22 a and 22 b, creating conditions where random failures can occur at the side seals 22 a and 22 b because of excessive force.

[0020] As shown in FIG. 2, the header 12 is heat sealed to the inner surface of the body portion 20 along a longitudinal strip 14 on the lip 16 thereby forming a seal between the lip 16 and the header 12. The heat seal is achieved through tight control of material tensions, temperature of seal heads, and pressure applied at the contact point, as to not deform the materials as they are being joined. The header 12 may be attached to the lip 16 using other means including adhesively bonding the header 12 to the lip 16. The header 12 is preferably attached to the inner surface of the body portion 20 of the bag 10 along a longitudinal heat seal 14, for example, using a modified rotary heat seal head attached to a sideweld wicketing bag machine. On some embodiments of the invention, including one where the header 12 extends further into the interior of the bag, a seal configuration can be employed where the longitudinal heat seal 14 will be formed using a multiple seal sealing head, resulting in two or more longitudinal seals spaced at various intervals down the interior body portion 20 that attach header 12 to the inner surface of the body portion 20. On another embodiment of the invention, seals 14 are made only at the lip 16 and the bottom of header 12. One other form of sealing header 12 to body portion 20 employs a seal device that produces raised points in various patterns on header 12 where it extends inside of body portion 20 that creates a condition of separation between 20 a and 12 whereby air blowing from a bag loader can easily penetrate between the layers 20 a and 12 to insure bag opening.

[0021] The header 12 is preferably formed from a non-heat-shrinkable film. As used herein, a non-heat-shrinkable film includes a film that may shrink a minimal amount upon the application of heat such as up to about five percent, whereas heat shrinkable film as known to those of ordinary skill in the art will shrink an amount that is substantially more. One preferred non-heat-shrinkable film is low density polyethylene. Other suitable materials include medium and high density polyethylene, polyesters, nylons, and polypropylenes. The non-heat-shrinkable film may be transparent or opaque and may include wording, graphics or other indicia, such as product information, instructions, or advertisement.

[0022] The header 12 may contain one or more wicket holes 18 that allow the bags 10 to be accurately stacked either on transfer pins or wickets to aid in future utilization of the stacked bags 10.

[0023] The preferred thickness of the materials used to form the bag may vary. For shrink bags, commonly accepted thickness ranges from 0.0006″ to 001″. It is widely known to those in the art of packaging films manufacture, that shrink bags using material thickness at the lower end of the thickness range tend to be more difficult to produce due to their lightness and their susceptibility to stresses induced by heat and tension.

[0024] The product to be packaged is placed in the interior chamber of the body portion 20 such that the relatively thick walls of the body portion 20 enclose the product while resisting tearing or puncturing by the product. As is known, a tray made from expanded polystyrene foam material may be used to package the product within the heat shrinkable bag 10. Alternatively, trays can be made from materials such as polypropylene (PP), CPET, PVC, and OPS, or, products may be placed within the bag chamber without the presence of a tray. The opening to the interior chamber of the body portion 20 is then heat sealed and the header 12 removed along with a small portion of body portion 20.

[0025] Referring now to FIG. 3, the bag 10 of the present invention may be formed using a modified sideweld bag making machine 30 having a rotary transfer device and a wicket conveyer. The bag making machine 30 is used in conjunction with a large roll of plastic heat shrinkable film 32. Film 34 to be used for the side walls 20 a and 20 b is drawn off of the roll and then folded onto itself using a folder 36 to begin forming the body portion 20.

[0026] The non-shrink header 12 is preferably attached to the body portion 20 of the bag 10 prior to advancing the body portion 20 into the hole punching section of the bag machine 30 where wicket holes are made in the header 12. Preferably, the header 12 is formed from a film material such as polyethylene that is stiffer than the material used for form the body portion 20 to aid in the stabilization and tracking of the bag 10 through the hole punching section of the machine. The header 12 is unwound off of a large roll 38 mounted to a secondary unwind stand that is positioned adjacent to the bag machine. The header 12 is fed into the body portion 20, using a header inserter 40 in between layers 20 a and 20 b. Together, the now joined materials are fed through the longitudinal sealing device 42 where seal 14 is made. The body portion 20 with the header 12 attached then advances to the hole punch section 44 of the bag making machine where hole punches are used to form holes 18 in the header 12 through which the transfer wicket pins on the wicket conveyer will eventually pass.

[0027] The body portion 20 (with the header 12 attached thereto) of the bag 10 then advances to the side sealer/separator 46 of the bag machine 30, which typically is a heated knife mounted in brackets that allow the knife to travel vertically and perpendicular to the material under construction. The hot knife melts through the folded film, simultaneously severing the folded film and sealing the trailing edge of the material to form a completed bag 10 and forming the leading edge seal on the folded film in anticipation of formation of the next bag 10 to be produced. During this phase of the process, a conventional wicketed heat shrink bag will slightly alter its position due to the effects of the heat. As the bag advances forward, it is picked up by vacuum arms that transfer the bag to the stacking section 48 where the wicket holes in the header of the bag are supposed to line up with pins 50 mounted on the stacking section 48. If the materials has shifted, the alignment of the holes is off, causing some of the bags not to be stacked on the pins 50. The misaligned bags eventually fall off the stacker section and end up as scrap. The bags 10 of the present invention, having a stiffer non-shrink header 12 do not shift when contacted by heat, thereby avoiding the misalignment with the pins 50.

[0028] The heat shrinkable bag described herein greatly reduces or eliminates failures in production and use of such bags generally caused by the heat stress and allows for more efficient production in the manufacture of the bags at a reduced costs, and reduced loss of bags and product at the packager.

[0029] The present invention also allows for precisely aligned stacks of wicketed bags in a bag machine having a rotary bag transfer mechanism and a wicketing conveyer. The stiffer polyethylene material used for the header 12 of the bag 10 produces a bag 10 that lays flatter on the user's bag loading equipment, thereby making it possible to package products faster and with less wasted bags than a conventional shrink bag.

[0030] Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible without departing from the spirit and scope of the present invention. Therefore the scope of the appended claims should not be limited to the description of the preferred embodiments described herein. For example, lighter thickness bags made of various materials can be manufactured at higher efficiencies if they incorporate a header made from more stable material, 

What is claimed is:
 1. A heat shrinkable bag for containing a product comprising: first and second side walls formed from heat shrinkable material and joined together to form a body portion having an opening for access into an interior chamber having an inner surface to receive and contain the product; and a header attached to the body portion that extends outwardly from the opening in the body portion, wherein the header is substantially formed from non-shrinkable film material that prevents distortion of the header during manufacture of the bag.
 2. The heat shrinkable bag of claim 1 wherein the header is attached to the inner surface of the interior chamber and wherein a portion of the header extends down into the interior chamber of the body portion.
 3. The heat shrinkable bag of claim 2 wherein the header is attached to the inner surface of the body portion using a thin longitudinal heat seal.
 4. The heat shrinkable bag of claim 1 wherein the first and second side walls are formed from a single sheet of heat shrinkable polyolefin film that is folded over upon itself to form a fold at one end and in which edges of the first and second side walls are heat sealed to each other to form the body portion.
 5. The heat shrinkable bag of claim 1 wherein the heat shrinkable material used to form the body portion is formed from biaxially oriented shrink polyolefins.
 6. The heat shrinkable bag of claim 1 wherein the header is formed from a non-shrinkable polyethylene.
 7. The heat shrinkable bag of claim 1 wherein the header has a thickness of between 1.25 and 3.0 mils.
 8. The heat shrinkable bag of claim 1 wherein the header includes wicket holes.
 9. The heat shrinkable bag of claim 1 wherein the heat shrinkable material of the side walls and the non-shrinkable film material have slip characteristics that promote a non-blocking interface between the header and the side walls, thereby promoting ease of separation between the header and the side walls when opening the bag for product insertion.
 10. The heat shrinkable bag of claim 1 wherein the header further comprises a slit path and is made from a material that when slit, will only propagate a tear along the slit path.
 11. A heat shrinkable bag for containing a product comprising: first and second side walls formed from a single sheet of heat shrinkable polyolefin film that is folded over upon itself to form a fold at one end and in which edges of the first and second side walls are heat sealed to each other to form a body portion having an opening for access into an interior chamber having an inner surface to receive and contain the product; and a header attached to the inner surface of the body portion along a thin longitudinal heat seal that extends outwardly from the opening in the body portion, wherein the header is substantially formed from non-shrink material that prevents distortion of the header during manufacture of the bag.
 12. The heat shrinkable bag of claim 11 wherein the heat shrinkable material used to form the body portion is biaxially oriented shrink polyolefins .
 13. The heat shrinkable bag of claim 11 wherein the header is formed from polyethylenes.
 14. The heat shrinkable bag of claim 11 wherein the header has a thickness of between 1.25 and 3.0 mils.
 15. The heat shrinkable bag of claim 11 wherein the header includes wicket holes.
 16. A method for producing a heat shrinkable bag for containing a product comprising the steps of: folding a single sheet of heat shrinkable polyolefin film over upon itself to form first and second side walls, wherein the second side wall has a lip extending above the top edge of the first side wall; attaching a header to the lip along a thin longitudinal heat seal such that the header extends outwardly from the side walls, wherein the header is substantially formed from non-shrink material that prevents distortion of the header during manufacture of the bag; and applying heat and pressure to seal two edges of the side walls to form a body portion having an opening for access into an interior chamber to receive and contain the product. 